ORCID Profile
0000-0001-6865-2871
Current Organisations
arcetri Astrophysical Observatory
,
Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Sensory Processes, Perception and Performance | Psychology | Behavioural Ecology |
Expanding Knowledge in the Biological Sciences | Expanding Knowledge in Psychology and Cognitive Sciences | Expanding Knowledge in Technology
Publisher: EDP Sciences
Date: 09-2020
DOI: 10.1051/0004-6361/202038133
Abstract: We investigated the ultraviolet (UV) spectral properties of faint Lyman- α emitters (LAEs) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint Universe. We used data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M UV of −18 and down to M UV of −16), low stellar mass (median value of 10 8.4 M ⊙ and down to 10 7 M ⊙ ) LAEs at redshift z ≳ 3. We computed various averaged spectra of LAEs, subs led on the basis of their observational (e.g., Ly α strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We searched for UV spectral features other than Ly α , such as higher ionization nebular emission lines and absorption features. We successfully observed the O III ] λ 1666 and [C III ] λ 1907+C III ] λ 1909 collisionally excited emission lines and the He II λ 1640 recombination feature, as well as the resonant C IV λ λ 1548,1551 doublet either in emission or P-Cygni. We compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly α equivalent widths, fainter UV magnitudes, bluer UV spectral slopes, and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in in idual spectra of z 2 galaxies. This suggests that weak UV features are likely ubiquitous in high z , low-mass, and faint LAEs. We publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.
Publisher: Oxford University Press (OUP)
Date: 21-12-2018
Publisher: Oxford University Press (OUP)
Date: 06-07-2012
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202140876
Abstract: Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Ly α , has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Ly α emission becomes increasingly challenging at z ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large s le of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Ly α emission. The s le of 2052 emission line sources with 1.5 z 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic c aigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full s le for UV emission features via emission line template matching, resulting in a s le of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Ly α ) UV emission lines increases with survey depth, and that the emission line strength of He II λ 1640 Å, [O III ] λ 1661 + O III ] λ 1666, and [Si III ] λ 1883 + Si III ] λ 1892 correlate with the strength of [C III ] λ 1907 + C III ] λ 1909. The rest-frame equivalent width (EW 0 ) of [C III ] λ 1907 + C III ] λ 1909 is found to be roughly 0.22 ± 0.18 of EW 0 (Ly α ). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IV λ 1548 + C IV λ 1551 we find that Δ v C IV ≲ 250 km s −1 , whereas Δ v Ly α falls in the range of 250−500 km s −1 which is in agreement with previous results from the literature. The electron density n e measured from [Si III ] λ 1883 + Si III ] λ 1892 and [C III ] λ 1907 + C III ] λ 1909 line flux ratios is generally 10 5 cm −3 and the gas-phase abundance is below solar at 12 + log 10 (O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full s le and in idual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log 10 (U) ≈ −2.5 and metal mass fractions that scatter around Z ≈ 10 −2 , that is Z ≈ 0.66 Z ⊙ . Value-added catalogs of the full s le of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.
Publisher: EDP Sciences
Date: 04-2019
DOI: 10.1051/0004-6361/201834565
Abstract: Deep optical spectroscopic surveys of galaxies provide a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at z ∼ 2 − 4.5. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble Deep Field South, Ultra Deep Field, COSMOS, and several quasar fields with other publicly available data from VLT/VIMOS and VLT/FORS2 to construct a catalogue of He II λ 1640 emitters at z ≳ 2. The deepest areas of our MUSE pointings reach a 3 σ line flux limit of 3.1 × 10 −19 erg s −1 cm −2 . After discarding broad-line active galactic nuclei, we find 13 He II λ 1640 detections from MUSE with a median M UV = −20.1 and 21 tentative He II λ 1640 detections from other public surveys. Excluding Ly α , all except two galaxies in our s le show at least one other rest-UV emission line, with C III ] λ 1907, λ 1909 being the most prominent. We use multi-wavelength data available in the Hubble legacy fields to derive basic galaxy properties of our s le through spectral energy distribution fitting techniques. Taking advantage of the high-quality spectra obtained by MUSE (∼10 − 30 h of exposure time per pointing), we use photo-ionisation models to study the rest-UV emission line diagnostics of the He II λ 1640 emitters. Line ratios of our s le can be reproduced by moderately sub-solar photo-ionisation models, however, we find that including effects of binary stars lead to degeneracies in most free parameters. Even after considering extra ionising photons produced by extreme sub-solar metallicity binary stellar models, photo-ionisation models are unable to reproduce rest-frame He II λ 1640 equivalent widths (∼0.2 − 10 Å), thus additional mechanisms are necessary in models to match the observed He II λ 1640 properties.
Publisher: American Astronomical Society
Date: 11-2022
Abstract: The Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY (CLASSY) provides the first high-resolution spectral catalog of 45 local high- z analogs in the ultraviolet (UV 1200–2000 Å) to investigate their stellar and gas properties. Here we present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (N iv ] λ λ 1483,87, C iv λλ 1548,51, He ii λ 1640, O iii ] λ λ 1661,6, Si iii ] λλ 1883,92, C iii ] λ 1907,9). Specifically, our aim is to provide accurate diagnostics for the reddening E ( B − V ), electron density n e , electron temperature T e , metallicity 12+log(O/H), and ionization parameter log( U ), taking the different ISM ionization zones into account. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all CLASSY targets. We find that UV density diagnostics estimate n e values that are ∼1–2 dex higher (e.g., n e (C iii ] λ λ 1907,9) ∼ 10 4 cm −3 ) than those inferred from their optical counterparts (e.g., n e ([S ii ] λ λ 6717,31) ∼ 10 2 cm −3 n e ([Ar iv ] λ λ 4714,41) ∼ 10 3 cm −3 ). T e derived from the hybrid ratio [O iii ] λ 1666/ λ 5007 proves to be reliable, implying differences in determining 12+log(O/H) compared to the optical counterpart O iii ] λ 4363/[O iii ] λ 5007 within ∼ ±0.3 dex. We also investigate the relation between the stellar and gas E ( B − V ), finding consistent values at high specific star formation rates (sSFRs log ( sSFR ) ≳ − 8 yr −1 ), while at low sSFRs we confirmed an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log( U ), but note that there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.
Publisher: American Astronomical Society
Date: 20-09-2022
Abstract: The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to those seen at high z ( z 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST’s Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii ] nebular emission. Despite changes in spectral resolution of up to ∼25% between in idual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N 20.
Publisher: American Astronomical Society
Date: 24-07-2019
Publisher: American Astronomical Society
Date: 27-07-2022
Abstract: Far-ultraviolet (FUV ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of le wavelength coverage, signal-to-noise, spectral-resolution, and s le ersity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N 1500 Å ≳ 5/resel), high-resolution ( R ∼ 15,000) FUV spectral database of 45 nearby (0.002 z 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY s le covers a broad range of properties including stellar mass (6.2 log M ⋆ ( M ⊙ ) 10.1), star formation rate (−2.0 log SFR ( M ⊙ yr −1 ) +1.6), direct gas-phase metallicity (7.0 12+log(O/H) 8.8), ionization (0.5 O 32 38.0), reddening (0.02 E ( B − V ) 0.67), and nebular density (10 n e (cm −3 ) 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a s le that is consistent with the z ∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to z ≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
Publisher: American Astronomical Society
Date: 25-07-2023
Abstract: Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at z phot ≃ 7.6, triply imaged by the galaxy cluster A2744 ( z d = 0.308). All three images are very compact, i.e., unresolved, with a delensed size upper limit of r e ≲ 35 pc. The images have apparent magnitudes of m F444W ∼ 25−26 AB, and the magnification-corrected absolute UV magnitude of the source is M UV,1450 = −16.81 ± 0.09. From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of L bol ≳ 10 43 erg s −1 and L bol ∼ 10 44 –10 46 erg s −1 , respectively. Based on its compact, point-like appearance, its position in color–color space, and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e., an active galactic nucleus at high redshift. We also discuss other alternative origins for the object’s emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified—and thus intrinsically even more compact—and that it occupies notably distinct regions in both size–luminosity and color–color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.
Publisher: American Astronomical Society
Date: 07-2021
Publisher: Oxford University Press (OUP)
Date: 30-12-2015
Location: Italy
Start Date: 2014
End Date: 12-2017
Amount: $360,000.00
Funder: Australian Research Council
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